1. Field of the Invention
The present invention relates to a magnetic tape cartridge, and more particularly to a magnetic tape cartridge in which a single reel with magnetic tape wound thereon is rotatably housed within a cartridge case, and in which a reel locking mechanism, for causing the reel to be in a locked state when not being used, is provided within a reel hub.
2. Description of the Related Art
In the existing magnetic tape cartridges, which are being used as storage media that are employed in external storage units for computers, etc., there is known a type where a single reel with magnetic tape wound thereon is rotatably housed within a cartridge case. This type of magnetic tape cartridge has only a single reel within the cartridge case. Because of this, when the magnetic tape is loosened by shock due to a fall of the cartridge, etc., the loose part cannot be absorbed and therefore there is a disadvantage that the magnetic tape will be damaged.
Hence, there has been proposed a magnetic tape cartridge equipped with a reel locking mechanism for restraining rotation of the reel when not being used. The reel locking mechanism is disclosed, for example, in Japanese Unexamined Patent Publication No. 11(1999)-238352. The reel locking mechanism is equipped with a locking member movable in the axial direction of the reel between a locking position and an unlocking position; a member for urging the locking member in a locking direction; and an unlocking member for moving the locking member to the unlocking position by being rotated integrally with the reel by the rotation-drive member of a cartridge drive unit.
The locking member is equipped with locking teeth, which mesh with locking teeth formed in the reel to forcibly lock rotation of the reel when not being used. That is, the locking member is constructed so that the magnetic tape is not tightened or loosened by shock due to a fall of the cartridge, etc.
This type of magnetic tape cartridge, incidentally, is often loaded into a cartridge drive unit so that the reel is horizontally held. However, in the case of an automatic loader with a large number of cartridges, for example, each cartridge is loaded into the cartridge drive unit so that the reel is vertically held. That is, each cartridge is vertically placed.
In that case, the cartridge case is positioned by the positioning means of the cartridge drive unit, and in order to prevent the outer periphery of the reel from contacting the inner wall surface of the cartridge case, there is a radial clearance of some magnitude between the inner wall surface of the cartridge case and the outer periphery of the reel. Therefore, if the cartridge is vertically placed, the reel will be moved downward by the amount of the radial clearance. Because of this, the center axis of the reel hub is shifted from that of the rotation-drive member of the cartridge drive unit, and consequently, there is a problem that the chucking operation of the rotation-drive member with respect to the reel hub cannot be performed.
The present invention has been made in view of the circumstances mentioned above. Accordingly, it is the primary object of the present invention to provide a magnetic tape cartridge which is capable of preventing chucking failure when it is vertically loaded into a cartridge drive unit.
To achieve this end and in accordance with the present invention, there is provided a magnetic tape cartridge comprising:
a cartridge case in which a single reel with magnetic tape wound on the outer periphery of a reel hub is rotatably housed;
a locking member, provided within the reel hub so that it is movable between a locking position and an unlocking position in an axial direction of the reel, for locking the reel to restrain rotation of the reel when not being used; and
a plurality of ribs extending in the axial direction and formed in the inner periphery of the reel hub;
wherein a first radial clearance between the locking member and the ribs at the locking position is set to a value smaller than a second radial clearance between the locking member and the ribs at the unlocking position.
In the magnetic tape cartridge of the present invention, each of the ribs may be provided with a stepped portion so that the height of the rib from the inner periphery of the reel hub becomes higher at the locking position than at the unlocking position. In addition, each rib may have an inclined surface so that the height of the rib from the inner periphery of the reel hub becomes higher at the locking position than at the unlocking position.
In the magnetic tape cartridge of the present invention, it is preferable that the locking member be provided with a protruding portion, which is opposed in close proximity to the inner peripheral surface of a flange of the reel at the locking position, for regulating core axis misalignment of the reel. It is also preferable that the protruding portion be provided at a position away from the outer peripheral portion of the locking member in the direction of the axis of the reel. For instance, a circumferential wall may be provided so that it extends in the unlocking direction from the outer peripheral portion of the locking member facing the aforementioned ribs and has a protruding portion at its upper end. In this case, when the aforementioned locking member is at the unlocking position, the protruding portion of the circumferential wall is not opposed to the ribs.
According to the present invention, the first radial clearance between the locking member and the ribs at the locking position is set to a value smaller than the second radial clearance between the locking member and the ribs at the unlocking position. Therefore, even if the reel is caused to move downward by the weight of the magnetic tape when the magnetic tape cartridge is vertically loaded into a cartridge drive unit, the ribs abut the outer peripheral surface of the locking member immediately and regulate the downward movement of the reel. As a result, the amount of the core axis misalignment of the reel hub with respect to the rotation-drive member of the cartridge drive unit is held down to a slight value. Thus, chucking failure due to the core axis misalignment is prevented.
In addition, the second radial clearance between the locking member and the ribs at the unlocking position is set to a relatively great value. Therefore, there is no possibility that during rotation of the reel, the ribs will make contact with the locking member.
According to the present invention, the locking member is provided with a protruding portion, which is opposed in close proximity to the inner peripheral surface of the flange of the reel at the locking position through slight clearance. In this case, the core axis misalignment of the reel with respect to the rotation-drive member of the cartridge drive unit can be regulated at two positions away from the direction of the axis of the reel, so that the effect of preventing core axis misalignment can be further enhanced.